Air purge valves are generally fitted to liquid conduits such as, for example, mains distribution lines or sewage distribution conduits and are designed to ensure the release of air or other gases from the conduits, thereby avoiding the production of air locks, for example, which would interfere with the flow of the liquid. Air flowing through a liquid supply line may, apart from causing mechanical damage to equipment fitted on the conduit, also cause malfunctioning of different devices such as flow meters, valves and the like.
Two different kinds of gas puree valves are known. In both kinds, a float is located in a housing which is coupled at a lower end thereof to the conduit to be vented and which is provided at its upper end with a venting outlet aperture. In the course of normal operation with the flow of liquid through the conduit, the housing falls with liquid and the spherical float is forced upwardly against the outlet aperture sealing the same. However, when air accumulates in the conduit, the float is displaced downwardly under its own weight thereby opening the outlet aperture with consequent venting of the air. Then, the housing again fills with liquid and the aperture is sealed by the float.
In a first kind of air purge valve, known as the automatic kind, the outlet aperture is of relatively small dimensions and the float is displaced downwardly responsive to air presence in the housing, thereby allowing for the continuous, automatic venting of the conduit. However, in view of the relatively small dimensions of the aperture, this automatic kind cannot cope with situations wherein large quantities of air have to be vented and when such a situation arises, not all the air is released and some of it passes into the line, potentially giving rise to an air lock.
The second kind of air purge valve is used in order to cope with the situation wherein sudden large quantities of air appear in the line (e.g. upon filling, an empty conduit system) and have to be discharged (released from the conduit, for example to the atmosphere). This type of valve is the so-called kinetic valve. This valve has a relatively large aperture through which large quantities of air can be rapidly and effectively vented. However, with such a kinetic valve, once the housing thereof has filled with liquid and the float has been pressed against the large aperture so as to seal it, the valve will only reopen once the pressure in the housing has dropped to atmospheric pressure and, in consequence, the kinetic valve cannot be used for the continuous release of small amounts of air, in particular when flowing at high pressure.
Gas purge valves combining the features of the automatic and the kinetic types have been designed, which effectively consist of a kinetic valve and, superimposed thereon, an automatic valve. With such combination-type valves, continuous release of relatively small amounts of air throughout operation take place through the automatic valve, whilst sudden bursts of large quantities of air are released through the kinetic valve. Such combined valves are nevertheless of relatively bulky and expensive construction.
U.S. Pat. No. 4,770,201 to Zakai, discloses a combined type of gas purge valve comprising a housing having a fluid through-flow aperture with a valve seating formed in the housing and bounding said aperture. A flexible closure membrane is secured at one end to the housing and is adapted to be biased, under fluid pressure in the housing, against the valve seating so as to seal the aperture. Membrane displacing means are secured to an opposite end of the membrane so that displacement of the displacing means in a first sense progressively detaches successive transverse portions of the membrane from the seating so as to open the aperture while displacement of the displacing means in an opposite sense allows for the membrane to become sealingly biased against the seating.
U.S. Pat. No. 4,082,106 to Butcher discloses a valve for automatically collecting and venting gases included in flowing liquid. The valve has a chamber in which air collects, a float in the chamber and a vent valve at the top operated by the float to vent the chamber when the liquid level falls. The vent valve has a convex or concave seat with apertures therein and is sealed by a flexible diaphragm which is peeled progressively from the seat to open the valve. The diaphragm may be annular and fixed at its outer periphery, being flexed by a coupling at its center, or may be fixed at the center and flexed by a coupling at its periphery.
It is an object of the present invention to provide a new and improved gas purge valve having a compact and inexpensive structure. In particular, the gas purge valve according to the present invention is suitable for discharging of significantly low amounts of gas, i.e. gas flowing through a conduit at significantly low pressure and at a low flow rate. However, the device will also discharge of gas flowing at high flow rate and at higher pressure. Still a further object of the present invention is to provide a gas purge valve of the specified type, suitable for mounting to liquid conduits with varied configurations such as a through-flow device or an appendix type.